1. Field of Invention
This invention relates to an optical scanning device or hologram scanner comprising holograms for deflecting an optical beam at high speeds, and more particularly to an optical scanning device capable of linear aberration free scanning for effective use in an apparatus for recording and displaying signals or images using optical signals.
2. Description of Prior Art
FIG. 1 of the drawings illustrates a conventional optical scanning device using holograms. The optical scanning device, or hologram scanner, comprises a hologram disk 3 composed of holograms 31,32,33, . . . etc, prepared by exposure to an object beam 1 emitted as a divergent beam from a point source and a reference beam 2 emitted as parallel rays. Beams 1,2 are indicated by dotted lines. When parallel beams fall on the holograms 31,32,33, etc, an image is reconstructed by a reconstructing beam 5 impinging on a focusing plane 4 which is scanned and which is disposed behind hologram disk 3, as depicted.
As hologram disk 3 rotates, the reconstructed image on focusing plane 4 moves thereon along an arcuate scanning line as shown, with the result that the image is distorted. Although optical scanning devices employing semiconductor lasers are highly effective for use in laser printers, no hologram photosensitive material is available which has a sensitivity at the wavelength (0.78 .mu.m, for example) of the semiconductor laser. Therefore, there has been no optical scanning devices using holograms for semiconductor lasers.